This invention relates generally to medical devices and more particularly to flexible, power driven catheters for intravascular surgery and other medical surgery and procedures.
In U.S. Pat. No. 4,445,509 (Auth) there is disclosed a recanalization catheter for cutting away hard abnormal deposits, such as atheroscleratic plaque, from the inside of an artery and while preserving the soft tissue thereof. That recanalization catheter includes a multi-fluted, rotary cutting head mounted at the distal end of the catheter and arranged to be rotated by a flexible drive shaft extending down the center of the catheter. The rotation of the cutting head is stated as producing differential cutting to effect the removal of relatively hard deposits from relatively soft tissue. The drive shaft is arranged to be rotated within the catheter by an electric motor coupled to the proximal end thereof. The drive shaft is disclosed as being a steel helical coil of approximately 0.05 inch (1.3 mm) diameter. Such a coil is stated in the patent to be successful in transmitting high rotational speed (greater than 25,000 rpm) in a controlled fashion and with mechanical security.
In order for a recanalizing catheter to have wide applicability of use in intravascular surgery, its length should be sufficiently large, e.g., 2 to 3 feet or more, while its outside diameter, at least adjacent the working end, is sufficiently small, e.g., 3-4 mm. Moreover the catheter should be able to bend through a minimum diameter radius of curvature of 3 inches or less, in order to reach small, remotely located restrictions, e.g., occlusions.
As will be appreciated by those skilled in the art the torsional shear stress produced on a flexible drive shaft (e.g., a wire) will differ for different composition wires, e.g., approximately 150,000 psi for steel wires, 70,000 psi for beryllium-copper wires. If the radius of curvature through which the drive shaft must bend is very small, e.g., less than 3 inches, high bending stresses will be induced therein. In order to reduce bending strain the diameter of the flexible drive shaft or wire must be made very small, e.g., 0.02 or less inches. If the restriction opening tool is to be operated at a high rate of speed, e.g., greater than 20,000 rpm, in order to provide sufficient power at low torque, the deleterious dynamic effects of critical whirl (e.g., undue vibration) and friction caused by high side loads on the bearing surfaces supporting the drive wire must be overcome or minimized while the positional neutrality (centering) of the drive shaft is maintained in order to insure that proper operation ensues. Flexible drive systems of the prior art appear to leave much to be desired from the standpoint of effectiveness and efficiency of operation in applications involving high speed, small diameter, and small radius of curvature.
In copending U.S. patent application Ser. No. 701,063, filed on Feb. 13, 1985, entitled Shaft Driven, Flexible Intravascular Recanalization Catheter, which application is assigned to the same assignee as this invention, and whose disclosure is incorporated by reference herein there is disclosed and claimed a flexible drive assembly for use with recanalization catheters which overcomes the above noted disadvantages of the prior art. To that end the drive assembly as set forth in that application is a flexible assembly which is arranged to be disposed within a very small diameter, elongated, flexible tubular member having a distal end at which a tool, e.g., a cutter, is mounted for high speed rotation. The drive assembly includes a flexible drive shaft, e.g., a continuous length solid bodied or tubular wire or group of wires, which is mounted within plural spaced bearings to enable it to be rotated at a very high rate of speed from a remotely located motor. The bearings each basically comprise ball-like members having a central through which the drive shaft extends. The ball-like bearing members are spaced apart by plural spacer elements at a distance no greater than one-half the wave length of the standing wave which would naturally result from the rotation of a correspondingly sized but unsupported wire at the rotational speed. Each spacer element basically comprises an elongated tubular member having a pair of flared ends. Each of the ball-like bearing members is located between the trailing flared end of one spacer member and the leading free end of the next succeeding, proximally located spacer. Thus, the bearings and associated spacers serve to keep the drive shaft centered even as the catheter is bent through a sharp radius of curvature, while also preventing the shaft from going into critical whirl. A cooling fluid is preferably provided throughout the interior of the tubular member to cool and lubricate the bearings and driveshaft.
While the invention disclosed and claimed in the above noted copending application is suitable for its intended purposes it is nevertheless somewhat complex in construction. Hence a need existed for a flexible drive shaft having a simple and inexpensive bearing system for supporting an elongated rotary drive element at a central or neutral position while the production of undue or excessive vibration which could interfere with the restriction opening procedure and resulting from critical whirl.
To that end in copending U.S. patent application Ser. No. 746,220, filed on June 19, 1985 entitled Spiral Wire Bearing For Rotation Wire Drive Catheter, which application is assigned to the same assignee as this invention and whose disclosure is incorporated by reference herein, there is disclosed and claimed catheters for introduction in a lumen in a living being to perform a procedure therein. Each catheter is an elongated flexible member having a distal end at which a working head is located. The working head is preferably rotary and is arranged to be rotated by a drive assembly. The drive assembly includes elongated drive means for the working head and which extends through the catheter from the working head to a first remote, proximal location. The drive assembly also includes elongated bearing means which extends within the catheter from a point adjacent the working head to a second remote, proximal location. One of the drive means or the bearing means is formed as a spiral of at least one wire wrapped about the other of said means, whereupon the drive means can be rotated freely with respect to the other means and to the catheter to effect the rotation of the working head. The drive means and the bearing means cooperate with each other to maintain the drive means at a neutral position within the catheter as the catheter is bent through any arc up to a minimum radius of curvature, while enabling the drive means to be rotated at a high rotational speed without resulting in undue vibration which would interfere with the procedure, e.g., artery revascularization, being carried out by the catheter.
Various United States patents relate to powered drive shafts, particularly flexible drive shafts and including spirally wound bearings. For example, U.S. Pat. No. 3,180,625 (Wyzenbeek) discloses a flexible shaft having an outer casing enclosing a rotating core and providing a mouth for a spirally wound bearing. The bearing including a rib for supporting the rotating core. U.S. Pat. No. 4,112,708 (Fukuda) discloses a flexible drive cable having a rotary flexible core member formed of plural strands. The core is supported in a tubular elongated liner member. In some embodiments the liner member is in the form of spirally disposed surfaces to provide plural lubrication grooves therebetween. U.S. Pat. No. 1,785,345 (Hasemann) discloses an elongated flexible shaft such as used with an automobile speedometer located within a casing forming a bearing for the shaft. The cable is supported by a strip formed in a spiral and made of a wear-resisting hard metal. U.S. Pat. No. 2,821,092 (Cordoro et al.) discloses a rotary drive cable to which is fixedly secured a spiral element. The element serves to hold and position the central core within a liner and is formed of Teflon.
While the devices in all of the foregoing patents may be suitable for their intended purposes, none appears suitable for high speed operation in confined, small radius of curvature applications, where drive element positional neutrality and resistance to vibration, (such as would be caused by critical whirl), is of major importance, such as exists in artery revascularization, and other surgical procedures.
Other prior art devices utilizing flexible drive shafts for conveying rotary power to a working head or tool are disclosed in the following U.S. Pat. Nos.: 1,481,078 (Albertson), 1,636,038 (Bolozsky et al.), 2,570,335 (Fitch), 2,761,297 (Buchsteiner et al) and 4,424,045 (Kulischenko et al).
In copending U.S. patent application Ser. No. 567,506, filed on Jan. 3, 1984, which is now U.S. Pat. No. 4,589,412, entitled Method and Apparatus for Surgically Removing Remote Deposits, which has been assigned to the same assignee as this inention and whose disclosure is incorporated by reference herein, there is disclosed and claimed a fluid powered flexible catheter for opening restriction, such as caused by atherosclerotic plaque, in blood vessels of living beings. Further aspects of that invention are disclosed and claimed in copending continuation-in-part application Ser. No. 682,393, filed on Dec. 17, 1984, which is now U.S. Pat. No. 4,631,052, entitled Method and Apparatus for Surgically Removing Remote Deposits, also assigned to the same assignee as this invention and whose disclosure is also incorporated by reference herein.
The catheters of all of the foregoing copending and coassigned patents are not only suitable for intravascular recanalization procedures, but also may be used to effect other important medical/surgical procedures as well. Thus, among the procedures for which said catheters can be utilized are the following: peripheral and coronary vascular recanalization via removal of plaque and/or dilatation of the blood vessel, dilatation of small bodily lumens, such as eustachian or fallopian tubes, removal of thrombi, destruction of stones, such as gall stones, kidney stones, bile stones, etc., and in situ valvulectomy. Those methods and catheters for carrying out those methods constitute the subject matter of this application.